Aberration
by Merely Perspective
Summary: After an experiment gone wrong, a scientist finds themselves in a completely different dimension chasing a creature that they created. In an attempt to somehow rectify their colleagues mistake, the scientist stumbles upon a demon who is intent on not letting them leave. Struggling against time and a supernatural force of nature, they'll have to make ends meet. Slight Mephisto/OC.
1. Prologue

**A/N:** _Good day ladies and gentlemen. I present to you a new fanfiction I have. The idea for this fic came into being after I read several OC fanfictions about people being put into the world of Ao no Exorcist as though it was an anime and that they already knew about it. So I thought to myself, 'well why not have it as another dimension?', and tah-dah, here we are. I am unsure as to whether this fic will contain romance as the main character isn't really a romantic sort of person. However, I did want to experiment with Mephisto meeting someone with a similar level of intelligence because let's face it, he's far too underrated and he needs his personality explored a bit more. I would like constructive criticism on this story if people would be willing to give it, and I appreciate you who happens to be reading this right now._

 **Disclaimers and such:** _I do not own Ao No Exorcist, the only things I do own are obvious things like the main character and the main storyline. This is rated mature for gore and possible mature content. This entire story is some what AU._

 _ **Inspiration Music:** "Mellifluous" by Oshi_

* * *

. : **Prologue** : .

" _Humans are far more capable that one might think._

 _Some are just far more capable than others. "_

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Her job was not for those with weak stomachs; and it certainly wasn't for those with morals. The job was a cruel one that entitled one to push their emotions aside and put the purpose of their work above all else. In some ways, they were not human and neither were their 'projects'. Well… Not after they were done with them.

Kriemhilde, well-known to her peers as Dr Schwarzschild, was not one to mess around in her field of work — After all, they were messing with the very fabric of space and time. Such work was not suitable for normal humans to trifle with, which is why they were specialists in their field of work.

The Hisakawa Facility — named after the very man who discovered that space-time could be manipulated through the use of man-made creations — was a laboratory carved underground a mountain range in the North of Japan. None of the scientists who worked there actually _knew_ where the metal fortress of sorts was exactly. Once you entered the structure, you agreed to leave the world behind. You did not return from the abyssal halls of the laboratory for the rest of your life.

Dr Schwarzschild, head scientist and engineer of the aptly named "Time Gate", stalked through the seemingly never ending halls of the man-made fortress. The trail of documents left behind her in her haste was picked up by the fumbling hands of one of the newbies as he crudely stacked it in his free arm. The woman murmured under her breath, her emerald eyes only flicking upwards when she turned a corner. Gradually, the unorthodox pair made their way through the halls to enter a mechanical elevator where the elder of the two slammed her slender fingers onto the keypad in the wall. A whirring sound was heard and the elevators lights flicked once before their vision was blanketed with darkness.

Something akin to unease tickled into the pit of Kriemhilde however she ignored it in favour of stabbing her index finger on the largest button of the keypad. Slowly, they began to descend into the lower reaches of the laboratory to which only the most loyal of scientists were allowed access too.

The scrawny man who had only just passed the last stage of boyhood shook a little and yet despite his timid appearance there was an undeniable sharpness to his oceanic gaze that was the true mark of a scientist. His name was of little importance but for the sake of manners she recalled that he was named Ito and rarely used it, often referring to him as 'boy'. Now his loyalty had been proved the brunette supposed he was worthy of her calling him his name, although it wasn't without mild distaste.

As her eyes flickered to him he gave her a slight inclination of his head, indicating that he acknowledged her as his superior and the woman arched an eyebrow. A blush bloomed across his cheeks and she swallowed the urge to recoil. 'Silly boy.', she thought. Wasting his affections on female who was clearly out of his league would only lead to his downfall. It was only a matter of time until the facility broke him in though…

Her attention was brought to the fact that they had reached the very bottom level of the laboratory and strode out of the lift, her companion scurrying along behind her in an attempt to catch up.

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"I don't really think that you understand the situation Miss Schwarzschild—"

"I understand perfectly fine." The said person cut him off.

"U-um, as I was saying… The scientists in this area could not have possibly predicted that experiment A3-56 would have the strength to break out of its containment field—"

Kriemhilde's green orbs hardened and she roared back at him, " ' _Not possibly predicted_ '!? This is a man-made, _dimension jumping_ creature with the ability to teleport itself across large distances! Pumping it full of sedatives it going to do nothing considering that these so-called scientists decided to give this abomination genes that enable it to adapt and become immune to all kinds of chemicals."

She was furious. No, scratch that, she was utterly _enraged_ to the point she was actually considering killing this man.

"I- I- I apologise Miss Schwarzschild, I won't let it happen again—"

A shrill scream echoed from behind them and the pair turn around onto to witness one of the most brilliant minds of their whole project become nothing but smear across the wall. Some of the blood even splattered across the brunette's glasses, but she wasn't worried about that, oh no. It was the fact that their creation, their abomination, stood only 100 or so metres away. It's humanoid figure distorted occasionally, the black pigment of its 'skin' blurring away into nothing occasionally only to reappear as its body reformed.

A3-59 was no ordinary experiment. It was _conscious_. It knew what it was doing. It knew that it was far more powerful than any of the other life forms surrounding it. And while it had no eyes, it could definitely sense them.

Without warning the man standing to the side of her let out the most incredibly high pitched scream and proceeded to flee like the hounds of hell were on his tail. Unfortunately for him, this being was something much worse than a measly hound of hell and it flickered into existence before the man before he promptly exploded.

Kriemhilde arched an eyebrow in vague amusement. Good thing A3-59 killed him, her fingers were literally twitching across a scalpel attached to the bag at her waist.

The creature tilted it's oversized head at her, and what she supposed as a tongue flicked out to hang by its pectorals. Yes, she could feel dread pooling in the pit of her stomach as it began to make its way towards her, but she did not move. Her pride prevented her from doing so and the scientist merely plucked her glasses off her nose and rubbed them clean on her lab coat.

She was more than aware about what might happen, but for some reason unknown to her A3-59 flickered away appearing in the corridor to the west of her and it continued to travel away from her.

This was the lowest floor, so where could it possibly be going...? It was too weak at the moment to teleport away fully since it was still flushing the toxins out of its body so why would it—

 _The time gate_.

The green-eyed woman almost screamed in a mix of frustration and horror. How dare this thing think it was able to use her machine? The sheer audacity of the creation was enough to make a snarl morph her beautiful features into something terrifying.

Dr Schwarzschild _ran_. And she rarely ever ran.

Desperation clawed at her insides, churning her stomach and intestines so much that she wanted to vomit. If A3-59 used the time gate, the collision of two dimension manipulating creations both trying to warp the fabric of space-time at the same time... This dimension would not only end up destroyed but the 15 years she put into this project would be obliterated. She would end up with nothing and none of her greatest achievements to show for it as both would be warped to another dimension or possibly destroyed.

Long hair fanning out behind her, her heels clacked loudly as she charged towards the 6th Dimension Sector, fingers flying across keyboards and keypads to get to the room where she knew it was going.

Upon reaching the final door and shimmying through it as it slowly opened, she witnessed the creature fingering the dashboard that stood next to the large circular gate and she screeched.

"Nein, **STOP**!"

It ignored her in favour of continuing its task and she stumbled forwards as the gate began to charge up, the outer ring flaring to life.

It was in these final moments that Kriemhilde realised she didn't care if she died. She'd spent far too long formulating, experimenting and calculating to let this _prick_ slip out of her grasp, and with her masterpiece no less.

Desperately, the albino flung herself at A3-59 as it appeared in the center of the gate, her vision exploding into white.

* * *

 **Quick OC Overview:** _Kriemhilde Schwarzschild, female, German, aged 42. A scientist who specialises in human experimentation, engineering and quantum astrophysics. She has straight brown hair that is usually tied up in a pony tail that falls to mid back, albino due to never getting any sunlight and has angularly-shaped green eyes. Severely short-slighted. Has a slight god-complex and quite the impressive ego._

 **A/N:** _Chapters will be posted 1-3 times per week._

 _~Merely Perspective_


	2. Chapter 1

**A/N:** _Here is the first official chapter of 'Aberration', an if you have skipped to this chapter then I'd appreciate if you went back and read the Prologue, it's vital to the whole storyline and you'll be very confused if you keep reading from this point onwards. On another note, the two other main characters have been introduced in this story._

 **Disclaimer and Such:** _I do not own Ao No Exorcist, the only things I do own are obvious things like the main character and the main storyline._

 **Inspiration Music:** _"Lost Translation" by Moods_

* * *

. : **Chapter 1** : .

" _Please wake me now if I am dreaming._

 _Wake me before I fall deeper into this abyss._ "

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Kriemhilde woke to the sound of birds twittering and the sensation of a summer's breeze against her cheek. For a moment it felt as though she was back in Rosenheim with her Papa, their family dog running around her in a clearing. Choking, she snapped open her eyes and clutched her chest. Was she dreaming? Was this all some elaborate ruse to trick her into a false sense of security?

She was _outside_.

For the first time in nearly 20 years the brunette breathed in pure, organic oxygen, not the stuff that was filtered through the catalytic converters of the many machines in the laboratories.

It made her feel a little sick, after all her body was not accustomed to such large amounts of oxygen, even if only 21% of the atmosphere was made up of it. Underground it had been a mere 19% and at the lowest level it dropped to 16%. It was enough to kill an untrained person, particularly if they were constantly running at full power for an estimated 20 hours a day.

Peridot orbs blinked rapidly, taking in the abundance of greenness and life that surrounded her fallen form. Picking herself up the scientist took a cautious step, her pale fingers travelling down to her waist to rest on a scalpel.

She had never thought she would ever see the world above ground again but here she was. And it was absolutely breathtaking.

As a small smile curled at the corners of her lips, the albino slowly dusted herself off and corrected the specs that lay precariously upon the end of her nose. There was no evidence of a synthetic environment of any kind, the air was far too clean and the light was too bright to be from that of a man-made source.

Twitching slightly at the realisation that she'd have to walk to find some way of knowing where she was, Kriemhilde began her long trek to make her way to some form of civilisation so she could get back on her feet.

Aware of a slight tingling sensation on the backs of her hands, the woman tucked her hands into the pockets of her lab coat and let her fringe fall forwards. Her skin was perhaps only a shade or two darker than white and it appeared that the sun was already causing her to burn. It had only been 10 minutes or so but the melanin in her skin might as well be non-existent due to many years underground. She doubted she'd ever get her light tan complexion back. Not that it bothered her in the slightest. She was a scientist; brains were much more favoured than beauty. But being beautiful made it easier for her to manipulate both her test subjects and her peers.

What a _terrible_ person she was.

Again, it did little more irk her that people thought that her personality wasn't the greatest, but the brunette knew her intelligence overshadowed it so it wasn't really a problem at all.

Among the wildlife she spotted a rather peculiar looking creature. Its body was bulbous, with short legs and arms too long for its body and a slobbering mouth full of sharp teeth. It was also pigmented a lime green tone with red markings which continued to baffle her but nonetheless, her green eyes sparkled with intrigue. The most odd thing about its profile was the leather harness that clothed it, a leash attached near the top.

Grinning maliciously, Kriemhilde slipped off her heels and stalked towards the flank of it, sliding a scalpel out of her bag. There were no such creatures in her own world, so she determined that she had been transported to another dimension. Its unusual make-up was a giveaway to that.

Twisting her wrist slightly so that the blade reflected the light from the sun and momentarily blinded the creature, the scientist pounced, positioning the scalpel so that it would strike the thing in its gizzards.

Her aim was true and as the deadly object slid into the animals flesh with a satisfying ' _shluck_ ' sound, the woman continued to slice the thing right up to where its neck should be. Unexpectedly, its organs did not explode out on to the ground so she could observe them. In fact, it just screeched with pain before erupting into black specks that faded away in to nothing.

Her eyes widened, and more possibilities came flying into her head. This thing had obviously not been made from physical matter considering the way it had exploded.

Pursing her lips disappointedly, she cleaned the blade on her lab coat and put it back where it belonged, walking off in the direction she was originally heading.

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Above the previously mentioned woman, a gold-eyed individual sat with an onyx thumbnail clicking against his teeth. Yes, he had seen her kill one of his favourite companions but he was not angry at her. He felt nothing aside from interest. He'd seen the look in her eyes, that wild calculating look as she plunged her knife into Behemoth. And just before he had witnessed her murderous act, he had seen the way she eyed his pet of sorts.

It was a look that was reminiscent of his elder brother's.

Amaimon was no fool. He knew his brother would be interested in this woman for entertainment purposes, but something felt _off_ about her. The demon king couldn't find a valid reason as to why he felt this way but it made him want to forget she even existed and move on.

Ignoring the odd feeling, he began to inspect her further, noting that she must've been a little older that she looked because when she smiled crows feet became visible around her eyes. Her waist was slim and her hips were large, it looked as though she had a soft figure but as his gaze trailed upwards, he noticed her breasts looked firm and rather perky for their size. She was obviously more athletic than her clothes let on.

He shook his head slightly. Gaze unblinking, he squashed the lust that had started to accumulate as he took in her bloodthirsty personality and admittedly attractive figure.

As the woman started to walk away, Amaimon jumped off of his perch and sniffed the air, landing where she once stood. Taking brief note of her scent, he bounced away, heading in a direction similar to the one where the brunette was heading. He had to see his brother. He had to check if _he_ knew she was here. He wanted to keep this woman to himself, he wanted to keep her a secret from his brother.

As he reached his destination he composed himself. His brother always knew when he was hiding something, even through his emotionless façade.

"Otouto~ What a pleasant surprise! What brings you here?" A deep voice purred, a dark intention hidden behind the words.

The earth king kept his face blank and refused to let any emotions flicker across his eyes. After all, eyes were the window to the soul.

Not that he had one anyway.

Monotonously, he queried, "Do you have any candy for me, Aniki?"

The chairman's expression crumbled away to reveal distaste.

"You've eaten the bag I gave you earlier? Amaimon..."

"Sorry, Aniki." It was just as emotionless as his previous sentences.

His elder brother rose from behind his desk, holding his hands behind his back as he glanced out the window, eyes suddenly alight with curiosity. Mephisto glanced back at Amaimon, his pale lips twitching with amusement.

"Someone has entered the barrier it seems..." The elder stated, an unusual look overtaking his angular features.

It was with that sentence that Amaimon's expression shattered and he ground his teeth together. Again. Something was stolen from him _again_. If his brother even saw that woman he would never let her go. He'd play with her until she broke.

Mephisto caught the look and the tension in his jaw, his amusement manifesting in the form of a grin.

"Do you know who this person is, Otouto?"

While it was spoken innocently, the earth king knew better. He knew he had two choices. He could either lie and hope that the woman left his brother's vicinity before he could find her, or tell the truth and be spared of his brother's wrath, should he find out that Amaimon lied to him.

The latter begged for him to pick it but the gold-eyed demon chose the wiser option. To tell his brother the truth.

His dotted eyebrows angled downwards as he directed his gaze at the floor, mumbling, "I don't know them, but I think I have seen them, Aniki."

The gentledemon's grin grew and Amaimon wanted to be sick. His inner demon howled in frustration.

"Oh? Do tell."

"It's a woman, Aniki. I saw her kill Behemoth."

Now this caught his brother's attention.

"She killed Behemoth?" He murmured disbelievingly, twirling a strand of indigo hair around his finger.

"Yes. She looked like a doctor or scientist..."

A question hung in the air, yet his brother did not have to speak it.

"...She's a human."

Some kind of barrier was broken and his brother let out a satisfied purring sound from the back of his throat that bordered on the edge of being animalistic.

Amaimon felt a weight crushing him, and he wanted to crumble. He felt humiliated, so utterly disgusted of himself. He'd reduced himself to nothing but rubble. Him, one of the seven demon kings of Hell.

"Where did you last see her?"

"..." Amaimon was tempted to give him the wrong place but thought against it. "In the forest to the south-east of here... She was walking pretty fast so she might be reaching the eastern edge of it soon..."

"Thank you dear Otouto~ You've been such a _good_ brother today." Dismissively, Mephisto threw a bag of sweets at his green-haired sibling and poofed away, top hat and white mantle in hand.

Glancing down at the colourful wrappers in the bag he now held within his grasp, Amaimon found he didn't want them and put them back down onto his sibling's desk.

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* * *

After only 15 minutes or so, the middle-aged female found herself nearing the edge of the forest, as the trees were a little sparser and the sound of cars could be heard. It would be foolish of her to go out into the populated streets with her lab coat and equipment on show. On such a warm day it would seem suspicious.

She really hoped she was not asleep and that this was some kind of wondrous dream. She really did start to believe that she was outside and not bound underground by her life's work. If Kriemhilde woke up now, she might just cry.

Crying. The act of shedding sodium chloride in the form of droplets from your eyes to demonstrate pain, relief, sorrow or happiness.

How foreign that word was.

The scientist tucked a strand of hair behind her ear and stopped walking, raising her hands to take off her lab coat.

"My, my... And who might you be, my dear?"

The question rang out to the left of her and the woman found herself scowling. She hadn't even noticed anyone following her despite being on high alert.

Turning with caution, her eyes flickered to the source of the voice, finding a peculiar looking man.

"It's common courtesy to give your own name first, Herr." Her tone was glacial, matching her icy gaze.

Turning fully to face this man, she took a moment to take in his features.

His profile was sharp, almost feminine, but his strong jaw and prominent Adam's apple suggested otherwise. Raising her gaze, she noticed his pupils were slightly slitted and the hue of his optics was unnatural. His ears were not just pointed, but slightly longer than your average humans. The brunette was tempted to blame these unusual characteristics on Williams syndrome and the sharp teeth within his mouth on hypohidrotic ectodermal dysplasia, but having both of those diseases was extremely rare and these features seemed almost natural on this man.

As she was eyeing him up, she noticed he was doing the same and picked up on the way his eyes lingered on the flesh cutters at her waist.

He broke the tension with a chortle, "Oya oya! Fiery I see. I happen to be the owner of this forest, but for future reference my name is Mephisto Pheles, my Lady."

"Mephisto... Pheles?" Kriemhilde responded quizzically.

"Indeed. Might I be so bold as to yet again ask for your name?"

Mephisto Pheles… _Mephisto Pheles_ … Where had she heard that before…?

"It's Doctor Schwarzschild."

The newly-named Mephisto Pheles quirked a brow at her antics and made his way towards her, but casually so not to startle the brunette.

Then it snapped into placed and she flinched, emerald hues widening as she stumbled backwards.

 ** _Mephistopheles_**.

The stories of her childhood came rushing back, hitting her with so much force that she nearly caved in on herself. Heavy pants forced their way through her lips and her eyes watered. Sometime long, long ago when her Papa read stories to her, stories of demons who came to take human souls. The name of such a story happened to be Goethe's Faust.

This man—no, this _creature_ was not created by the mind of a human. He truly existed. And it made sense because logically, how could any human ever hope to form such mellifluous words and be in possession of a vast amount of knowledge that the likes of no mortal had ever seen. This being of incredible strength who defied the very laws of physics, stood before her with nothing but a grin on his admittedly devilishly handsome face.

As he stepped towards her, he could surely see the recognition in her eyes as she looked at him and the gargantuan hurricane of confusion that brewed within her. She had never felt so vulnerable in her entire existence as he stared at her in this moment, bemusement contorting his features.

"My Lady, are you alright?" False concern laced his tone as the demon continued to move forwards and placed a single digit underneath her chin.

The demon touched her, as if only to confirm he was real and his one finger turned into a hand. He cupped her chin gently and brought her slowly up to his level, his soft touch beguiling his true strength

Kriemhilde looked up at him through her lashes.

"I know what you are."

Laughter burst from the demons lips, lips that were only 4 inches approximately away from her own.

"Really now? What am I then, _Doctor Schwarzschild_?"

The words that spilled from her lips next stunned the demon king so much he burst into peals of laughter.

"An aberration."

His laughter swallowed the clearing they were in with its sheer loudness.

Kriemhilde noticed that he was in fact breathing as he expressed his amusement and there was a very slight flush to his cheeks, most likely due to the heat. Each strand of Mephisto's hair caught in the delicate breeze and his weight rested more on his left foot. While this visual evidence might make him seem living, she knew better.

"I have certainly never been called that before." He admitted, breathing a little heavier with a smile still lingering on his face.

Without warning, the woman slid her finger through one of the button holes on his jacket to undo his top button and she placed her palm on his chest beneath his jacket. Underneath her pale hand a faint beating could be felt, yet she kept her hand in place for fear that is was simply a trick of her mind.

The purple-haired demon's throat gave a low rumble, "Trying to undress me already? If you were that eager you could have just asked. It would be a _pleasure_ to be in the company of such a beautiful young woman..."

The scientist shot him an incredulous look, letting out a quiet chuckle at the last part of the demons sentence.

"Young? Herr Pheles..."

She pulled her hand away from his chest slowly, her crooked grin gradually growing wider.

"...I am 42~"

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 **A/N:** _That's a wrap. Constructive criticism and opinions on the story would be a godsend._

 _~Merely Perspective_


End file.
